1. Field of the Invention
This invention relates to a process of preparing esters of sterically hindered resin acids, rosins, resins, and derivatives containing them by reacting a quaternary ammonium salt thereof with an alkyl or alkenyl polyhalide.
2. Description of Prior Art
Esterification of resin acids, rosins, resins, and derivatives containing them is difficult because of the steric hindrance of the diterpene acids and derivatives contained therein, e.g., abietic acid, isopimaric acid, pimaric acid, dehydroabietic acid and related skeletal types. Simple esters such as methyl esters can be prepared for laboratory use with expensive reagents such as diazoalkanes or dialkyl acetals of dimethylformamide under relatively mild conditions, e.g., room temperature (25.degree. C.). However, commercial processes use other reagents and require higher temperatures. If more complex esters, i.e., those of polyhydroxy alcohols such as glycerol and pentaerythritol are made, even higher temperatures are required (about 250.degree. C.). Present commercial processes involve esterification with alcohols and acids, using reagents that are different from those of the present invention.
Although the reaction of alkyl monohalides with alkali metal salts of carboxylic acids is possible, the reaction is of little importance commercially because of problems in solubility and reagent decomposition.
Mills et al. Chem. Ind. 2144 (1962) disclose the synthesis of esters by the reaction of lower alkyl halides and tertiary amine salts of carboxylic acids at about 150.degree. C. For example, the reaction of methylene chlochloride with the triethyl amine salt of the monobutyl ester of phthalic acid for 12 hours gives a 72% yield. No esters of resin acids, resins, rosins, or derivatives thereof are disclosed. No quaternary ammonium salts are disclosed for use in the process.
Holmberg et al., Tetrahedron Letters, No. 27, 2303 (1975), disclose the reaction of tetrabutylammonium salts of carboxylic acids with methylene chloride taking several days to complete. The use of sterically hindered trimethylacetic acid is disclosed. There is no disclosure of resin acids, resins, rosins, or their derivatives.
Crane, U.S. Pat. No. 1,513,802, discloses a process of forming artificial resinous bodies by reacting an aromatic compound having haloalkyl substituents on the benzene ring with a resin acid in which a metal is substituted for the acid hydrogen. Typical aromatic compounds disclosed are benzyl chloride and chlor-xylene, resins disclosed are pine rosins which contain, inter alia, abietic acid. There is no disclosure of alkyl or alkenyl halides or of any reaction with a quaternary amine salt.
Johnston, U.S. Pat. Nos. 1,749,482 and 1,749,483, disclose a process of forming alkyl esters of commercial abietic acid or abietic acid as present in rosin with an alkyl halide such as ethyl chloride or bromie in the presence of an alkali for one-half hour at elevated temperatures and pressures. There is no disclosure of using a quaternary amine salt of the acid as a reactant.
Borglin, U.S. Pat. No. 2,012,622, discloses an esterification process of reacting a monohydric heterocyclic alcohol and abietic acid with heat and an optional catalyst, e.g., para-toluene sulfonic acid. There is no disclosure of the use of a quaternary amine salt.
The references disclosure certain aromatic, alkyl and heterocyclic esters of the acids in rosin, i.e., diterpene resin acids.